1. Field of the Invention
The present invention relates to a method of driving a motor-driven shutter for a camera.
2. Description of the Related Art
In a typical conventional method of driving a motor-driven shutter for a camera, a travelling member is rotated in one direction by activating a motor so that, during the rotational movement of the travelling member, a sector opening cam provided on the travelling member engages an engagement pin provided on a sector opening lever. As the travelling member continues to rotate, the engagement pin rides on the sector opening cam, causing the sector opening lever to pivot, and thus opening the shutter. After the engagement pin has reached a predetermined position on the sector opening cam, the motor is reversed to cause the travelling member to rotate in the opposite direction and return to the previous position.
The above-described conventional method suffers, however, from the following problems. Namely, in the prior art method, immediately after coming into contact with the sector opening cam, the engagement pin rides on the cam, thus suddenly opening the shutter which has been closed. Since the static friction, that is, the force required to move the shutter when closed, is considerably large, a great deal of inertia acts on the shutter when opened suddenly. In addition, the load is increased by the engagement pin riding on the cam. For this reason, the shutter undulates and this makes it impossible to obtain an adequate degree of aperture accuracy and leads to variations in the degree of opening of the aperture.
To solve this problem, it is conventional practice to reduce the change in the slope of the cam so that the shutter is gently operated during the initial stage of the shutter opening operation. This conventional practice, however, has the problem that the operating stroke of the cam increases.